| electric fuel pump question [message #131372] |
Tue, 21 June 2011 21:10  |
larry.whisler
Messages: 356
Registered: August 2005
Karma: 8
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All,
I am doing away with the mechanical fuel pump and installing electric fuel pumps back near the tanks.
I am running a red wire from the fuse block utilizing the windshield washer pump circuit which is rated at 10 amps.
The red wire will run to the oil pressure switch (NO terminal) and black wire from the starter to the switch (NC terminal).
And blue wire from the switch to the pump. The fuel pumps are rated at 10 amps each and will run only one at a time controlled by a 5 pin relay and the windshield washer pump is rated at 10 amps.
Should I still use a 10 amp fuse on this circuit or increase to 15 or possibly 20?
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thanks in advance for the advice
larry ( electrically challenged ) whisler
[Updated on: Tue, 21 June 2011 21:11] Report message to a moderator |
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| Re: electric fuel pump question [message #131373 is a reply to message #131372] |
Tue, 21 June 2011 21:15  |
PettyVTX
Messages: 363
Registered: April 2011
Location: Winder Ga.
Karma: 1
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Senior Member |
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What pumps are you using I have a holley blue but i think it may be too much pressure. I may have to install a regulator.
Ex Avion now looking for a 23'
Jeep Wrangler Towd
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| Re: electric fuel pump question [message #131402 is a reply to message #131372] |
Wed, 22 June 2011 02:13 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I run my single Carter P4070 on a 3 amp fuse. I measured the current and it draws less than 1.5 amps. I have never blown the 3 amp fuse i run it on. If that size bothers you then go to a 5 amp fuse. I like to fuse things at around 150% to 200% of their normal draw. Installing larger fuses will not stop the pump from running but in going too large you are giving up the protection that a fuse is suppose to supply.
You did not state what model pumps you are using so all I can go by is what mine draws. If you want to check the current draw on yours, install and wire the whole thing. Then remove the fuse and install a VOM on the amp scale across the fuse connections and turn on the key. Now read the meter and that will be your maximum current draw. Start the engine and watch the meter as you bring up the engine speed. The draw will go DOWN slightly. The amount is insignificant. It took me a while to figure out why this is. But that is not important in this discussion.
Finally, you did not state the year of your coach. If you have a later coach with an HEI distributor, then there is an unused terminal on your starter solenoid. This connection will supply +12 volts only when cranking and nothing at all other times. Run the wire from the N/C side of the oil pressure switch to the starter solenoid unused terminal. This will allow you to add a push button prime button inside the coach at a later date should you want one.
To add a prime push button all you do is to hook one side of the prime push button to +12 volts and the other side to that same solenoid connection.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: electric fuel pump question [message #131487 is a reply to message #131429] |
Wed, 22 June 2011 15:48 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| larry.whisler wrote on Wed, 22 June 2011 10:02 |
Ken,
The coach is a 76 Glenbrook.
I am using the Carter P4070 pumps. I had already connected the Normally closed circuit on the switch to the terminal on the starter that you referred to.
My fuel selector valve was defective and needed to be replaced.
So, rather than replace the valve, I decided to install two pumps, one for each tank. They will be controlled by the five pin relay and the selector valve voltage will operate the coil on the relay. Looking at the cost of the valve versus the cost of additional pump was not much more. Plus now I have a backup pump.
Normally closed on the realy will operate the "main" pump, and normally open circuit will operate the "auxillary" pump.
I have teed the fuel lines with check valves to prevent back flow to the tanks.
I decided to use the the windshield washer circuit since the washer was the only item on the circuit and it would be an easy check if there was an engine problem to see if the fuse had blown.
larry
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I have no problems with anything in your design.
In my case I am using the P4070 as a boost pump and still have the mechanical one in place. I use a lighted rocker with the light powered directly off of the power lead to the pump. If I blow a fuse or for any other reason loose power to the pump, the light in the switch will not turn on.
This approach will not work in your case. I like your dual pump approach. I at first questioned getting power off of the washer pump circuit. Now I understand your logic. I think Ken H. is running dual pumps on his GMC.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: electric fuel pump question [message #131580 is a reply to message #131520] |
Thu, 23 June 2011 04:41 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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My fuel pump is fused. The lead to the starter is not. The lead to the starter is seldom used and then only for a brief period of time so I did not bother fusing it.
BTW, there are several things on the GMC that are not fused except for the inline fusible link up front. The ignition system, and the starter solenoid are two of them. When I rewired my coach after my engine fire, I installed 4 fuses up front and clearly labeled each of them. They were the ingition system, the electric choke, electric fuel pump and a spare where I keep a spare 5 amp fuse. The others all have 3 amp fuses in them.
Also a low current fuse does not like vibration and fuses blow by creating heat and melting. For two these reasons I would not put a low current fuse anywhere physically attached to the engine. Go ahead and try it if you want. If some day it refuses to start check the fuse first thing. If you add the momentary prime button I talked about, you could start the engine with the starter fuse blown and fix it later if necessary.
These are just some ideas for you. There are many ways to accomplish what you are doing.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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